Learn Hardcore Croatian: Sunce sja iznad grada. - The sun is shining above the city.

Sunce = the sun (neuter noun)
sja = shines / is shining (3rd person singular present of sjati, “to shine”)
iznad = above, over (preposition)
grada = of the city (genitive singular of grad, “city”)

Why is there no article before Sunce?

Croatian has no articles. Definiteness is understood from context, so Sunce naturally means “the sun” here.

What case is grada, and why is it used?

Grada is genitive singular of grad. The preposition iznad (“above”) requires the genitive, hence iznad grada (“above the city”).

Could I say nad gradom instead of iznad grada?

Yes. Nad also means “above/over” but it takes the instrumental: nad gradom. Nuance is minimal here; both are natural. Some speakers feel nad can sound a bit more immediate/physical, but in this sentence either works.

What verb is sja from, and are there alternatives?